Various types of hearing prostheses may provide people having different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural hearing loss. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea, where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
People with some forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing aids. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sound into the person's ear. Vibration-based hearing aids typically include a small microphone to detect sound, and a vibration mechanism to apply vibrations corresponding to the detected sound to a person's bone, thereby causing vibrations in the person's inner ear, thus bypassing the person's auditory canal and middle ear. Vibration-based hearing aids include bone anchored hearing aids, direct acoustic cochlear stimulation devices, or other vibration-based devices.
A bone anchored hearing aid typically utilizes a surgically-implanted mechanism to transmit sound via direct vibrations of the skull. Similarly, a direct acoustic cochlear stimulation device typically utilizes a surgically-implanted mechanism to transmit sound via vibrations corresponding to sound waves to generate fluid motion in a person's inner ear. Other non-surgical vibration-based hearing aids may use similar vibration mechanisms to transmit sound via direct vibration of teeth or other cranial or facial bones.
Each type of hearing prosthesis has an associated sound processor. One basic sound processor provides an amplification to any sounds received by the prosthesis. However, in other example hearing prostheses, the processor present in the hearing prosthesis may be more advanced. For example, some processors are programmable and include advanced signal processing functions (e.g., noise reduction functions).
A traditional sound processing system includes a signal input, a variety of processing modules, and an output. Typically, the audio signal feeds into a linear combination of processing modules. Each processing module has a specific function to perform on the audio signal. Additionally, the recipient of the prosthesis may be able to enable at least one processing mode for the hearing prosthesis. When the recipient selects at least one processing mode, a subset of the processing modules are selectively enabled or disabled based on the chosen processing mode. Further, the selection of at least one processing mode may modify parameters associated with processing modules. Thus, in the traditional processing system, once at least one sound processing mode is selected, the prosthesis will continue creating an output based on the selected sound processing mode(s).
In the traditional processing system, an Environmental Classifier may be located at one place in the signal path, typically using a microphone signal as input. Depending on the environment detected (e.g. either Noise, Speech, Speech+Noise, Music, etc.), an algorithm and parameter control module then decides what signal processing modes of the signal path to enable or disable, what parameters to change, and does this for the whole signal path. One potential disadvantage of such a scheme is that a classification decision is made only once.